RMS has been recognized as one of the most common malignant soft tissue tumors afflicting children, adolescents, and young adults. Because these tumors are small-, round-cells, it is very difficult to differentiate them from tumors such as Ewing's sarcoma, neuroblastoma, nephroblastoma and malignant lymphoma. Therefore, the diagnosis of childhood RMS is sometimes very difficult.Since the human muscle determination gene Myo-D was found to be expressed in several human RMS cell lines, cultured primary RMS tumor explants, biopsies of tumor and normal skeletal muscle tissues, but not in other non-muscle tissues and tumors, MyoD can serve as a differential marker to distinguish RMS from other small-, round-cell tumors of soft tissues. The primary goal of this application is to produce a panel of MAbs against human Myo-D protein in mutagenic differentiation. Specific aims of this application are: l) to generate a panel of MAbs recognizing human Myo-D protein, 2) to characterize these Myo-D-specific MAbs with authentic Myo-D protein, and 3) to evaluate the clinical values of these MAbs in the diagnosis of RMS.